1. Field of the Invention
The present invention relates to a pulse detecting device using a piezoelectric element as a detection element and an ultrasound diagnostic apparatus using the piezoelectric element.
2. Description of the Related Art
Important information that can be applied to the diagnostic of a disease is included in the pulse of a living body. Thus, recently, the following system is studied in a medical facility such as a hospital. That is, in this system, a portable type pulse detecting device is put on a patient's wrist, and then pulse detection data of the patient that is transmitted from this portable type pulse detecting device is received in a hospital to evaluate a state of the patient. It is effective to use the piezoelectric element for miniaturization and weight reduction of the pulse detecting device. Thus, based on the application to the above system, the development of the pulse detecting device using the piezoelectric element has progressed. In addition, an ultrasound diagnostic apparatus for obtaining information of a living body or an object using ultrasound is well known. This ultrasound diagnostic apparatus irradiates (transmits) an ultrasound into a diagnostic portion of a person to be examined or a diagnostic object, detects an echo produced by reflecting the ultrasound by the diagnostic portion, and obtains information with respect to the diagnostic portion in accordance with this detection result.
A conventional pulse detecting device 100 using the piezoelectric element is shown in FIG. 32. As shown in the drawing, in the pulse detecting device 100, two piezoelectric elements 110 and 120 are embedded in resin (or gel) 130 and fixed therein. Here, metal electrodes (not shown) are formed on both surfaces of the respective piezoelectric elements 110 and 120 in a thickness direction. Also, although not shown, drive voltage applying probes (terminals, lead wirings and the like) are connected with both electrodes of the piezoelectric element 110 and voltage signal outputting probes (terminals, lead wirings and the like) are connected with both electrodes of the piezoelectric element 120.
Also, for example, a pulse detecting device using an ultrasound transmits the ultrasound to the radial artery of a person to be examined and obtains a waveform of a pulse wave and a pulse rate from changes in a amplitude and a frequency of an echo.
Then, at an examination in a hospital, the pulse detecting device 100 is used to detect the pulse of a patient. With respect to details, when the drive voltage is applied to both electrodes of the piezoelectric element 110, the piezoelectric element 110 is excited to generate the ultrasound. The generated ultrasound is transmitted into a living body through the resin 130. The ultrasound transmitted into the living body is reflected by a blood flow of the living body and the reflected ultrasound is received in the piezoelectric element 120 through the resin 130. At this time, a change in a frequency due to a Doppler effect of the blood flow is produced between the ultrasound transmitted from the piezoelectric element 110 and the ultrasound received in the piezoelectric element 120. In addition, since the velocity of the blood flow is changed in synchronization with the pulse, the pulse of the living body is detected from the change in the frequency of the ultrasound.
Now, in the above pulse detecting device using the piezoelectric element, in order to improve the receiving sensitivity of ultrasound, it is necessary to locate the piezoelectric element 110 for transmitting the ultrasound and the piezoelectric element 120 for receiving the ultrasound with high precision.
The above pulse detecting device 100 is manufactured by arranging two piezoelectric elements 110 and 120 in predetermined positions of a mold and then pouring the resin 130 into the mold. However, When the resin 130 is poured into the mold, there is a possibility that positions and location angles of these piezoelectric elements are shifted, and thus there is a problem that a high precision arrangement of the piezoelectric elements is difficult.
Therefore, there is a possibility that the quality of the conventional pulse detecting device 100 is varied.
Also, generally, in the pulse detecting device using the piezoelectric element, in order to improve the receiving sensitivity of ultrasound, it is necessary to locate the ultrasound transmitting piezoelectric element and the ultrasound receiving piezoelectric element with high precision. Also, if the ultrasound is propagated through the inner portion of a substrate and then directly received in the ultrasound receiving piezoelectric element, this causes a noise and further strengths of a transmitting wave and a receiving wave to the blood flow, which are required for measuring the pulse are decreased. As a result, the detection sensitivity of the pulse is reduced. Therefore, in order to improve the detection sensitivity of the pulse, it is necessary to make a structure in which the ultrasound does not easily propagate through the inner portion of the substrate and then directly received in the ultrasound receiving piezoelectric element. Further, as the resin 130 becomes thicker, the strength of the ultrasound transmitted to the blood flow in the living body is decreased.
However, the above pulse detecting device 100 is manufactured by arranging two piezoelectric elements 110 and 120 in predetermined positions of a mold and then pouring the resin 130 into the mold. Accordingly, there are the following problems.
(1) When the resin is poured into the mold, there is a possibility that positions and location angles of these piezoelectric elements are shifted, and thus there is a problem that a high precision arrangement of the piezoelectric elements is difficult. Therefore, there is a possibility that the quality is varied.
(2) Since the pulse detecting device has a structure that the ultrasound is directly and easily received in the receiving piezoelectric element through the resin, there is a limitation in the detection sensitivity of the pulse.
(3) Since it is difficult to manufacture the resin 130 thin, there is a limitation in the detection sensitivity of the pulse.
Also, with respect to the ultrasound diagnostic apparatus, there are the same problems as in the pulse detecting device as described above.